Apparatus for use in administering intermittent positive pressure breathing therapy



May 28, 1968 N. F, Br-:AsLEY APPARATUS FOR USE IN ADMINISTERING INTERMITTENT j POSITIVE PRESSURE BREATHING THERAPY Filed Feb. 7, 1966 United States Patent O 3,385,295 APPARATUS FOR USE 1N ADMINISTERING DJ- TERMITTENT POSITIVE PRESSURE BREATH- ING THERAPY Noel l5". Beasley, Santa Monica, Calif., assignor to Puritan Compressed Gas Corporation, Kansas City, M0., a corporation of Missouri Filed Feb. 7, 1966, Ser. No. 525,495 Claims. (Cl. 12S-145.8)

This application relates to respiration apparatus and more particularly to improved apparatus of this type for use in administering intermittent positive pressure breathing therapy.

Intermittent positive pressure breathing, commonly known as IPPB, is a type of assisted breathing for patients who are breathing spontaneously at a self-controlled rate and rhythm. Such therapy has widespread acceptance as an effective means of relieving and treating many respi-ratory disorders.

In IPPB therapy, there are two phases in each complete breathing cycle, an inspiratory phase and an expiratory phase. The patient initiates the inspiratory phase by making a slight inspiratory effort, as in normal breathing. Gas comprising air or air enriched with oxygen, or in some cases an admixture of such gas and vaporized or nebulized medication, is then supplied to the lungs under a mild pressure to achieve ventilation. The inspiratory phase continues, preferably, until full and even ventilation has occurred. As this condition is approached, the flow of gas to the patient drops olf rapidly to a low level and eventually to a so-called terminal flow. This terminal flow is the flow taking place just at the end of the inspiration.

The expiratory phase is a passive phase in which the system pressure is rapidly reduced, preferably to ambient pressure, and the lungs are vented to the atmosphere. Expiration then occurs spontaneously, asin normal breathing, because of the elasticity of the lung-thorax system to complete a given breathing cycle.

It is desired that apparatus for administering such IPPB therapy have certain operational characteristics. One such characteristic is that the patient-effort required to initiate inspiration be no greater than that exerted in normal breathing. This characteristic is commonly known as sensitivity, it :being desired that the apparatus have a high sensitivity. It is also desirable that the peak flow capacity of the apparatus be relatively high. This stems from the fact that the average patient has a high ow requirement near the start of inspiration. His requirement thereafter progressively decreases, and, therefore, flow likewise decreases as system pressure increases, to the terminal iiow which, as noted above, takes place just at the end of inspiration.

Another desirable operational characteristic is that the apparatus have a very low terminal flow. This enables full and even ventilation of the alveoli to be achieved before the apparatus cycles into its expiratory mode of operation. By way of explanation, the lungs comprise a network of small passages of varying resistance leading to the alveoli. With a low terminal flow, pressure is maintained on these passages during the inspiratory phase for a sufiicient time to insure that the desired ventilation of `the alveoli is achieved.

Beside these operational characteristics, there are many other important considerations to be borne in mind in the design and manufacture of respiration apparatus. In view of the nature of such apparatus, it is apparent that reliability is a highly important feature. Experience has shown that reliability is diflicult, as Iwell as costly to obtain with respiration apparatus embodying conventional valving mechanisms with numerous critical moving parts.

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Manufacture to` close tolerances, closely controlled inspection and testing and the like, are all required in order to achieve the `desired end with most types of apparatus heretofore available. Often costs are prohibitive and, even assuming they are not, there is still the problem of potential abuse during use, resulting in malfunction. Thus, it will be readily appreciated that it is highly desirable from both reliability and cost standpoints to eliminate critical moving parts.

In view of the foregoing, it is a primary object of this invention to provide improved respiration apparatus for use in administering IPPB therapy which is highly reliable 1n operation.

Another object is to provide improved respiration apparatus of the type described which is simple in construction and may be mass produced by conventional methods at an extremely low cost.

A further, more specific object is to provide such respiration apparatus which has no critical moving parts.

Still another object of the invention is to provide respiration apparatus of lthe subject type further characterized by high sensitivity, high peak ow capacity and low terminal liow.

These and other objects, features and advantages of the invention will be better understood by referring to the following detailed description taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a semi-schematic view of the presently preferred embodiment of the invention, with the various elements being shown in the positions occupied in the expiratory mode of operation;

FIGURE 2 is a fragmentary view of the sensing unit illustrated in the right-hand side of FIGURE 1, in the condition which it occupies in the inspiratory mode of operation of the apparatus.

Referring to the drawing, the apparatus of the invention, as illustrated in FIGURE 1, controls the flow of pressurized gas from a source 10 through ya conduit system including a main conduit 12 land a delivery conduit 14. The main conduit 12 is coupled to the source and has a yvent opening 416 to the atmosphere, while the delivery conduit leads from the main conduit to delivery means 1:8. Flow from the source lll is continuous, and is alternately through the main conduit 12 out the vent opening 16 to the atmosphere during expiration and through both conduits 12 and 14 to the delivery means 1S during inspiration.

In order to achieve such flows during the respective phases of the breathing cycle, a vent valve 20 is provided for closing the vent opening 16 intermittently. It will be appreciated that when vent valve 20 is `operative to close the opening 16, the apparatus is in its inspiratory mode of operation with flow taking place from the source 10 to the delivery means 18. On the other hand, the inoperative period of the valve 2t) during which gas is exhausted through the vent opening 16, corresponds to the expiratory mode of operation.

Control means, shown within the dotted line enclosure so Idesignated in FIGURE l, are provided for operating the vent valve 16 in the manner previously described and thereby producing the desired cyclic operation of the apparatus. Briefly, such means comprise la sensing unit 22, a venturi 24, and an inspiration-start valve 26. Both the inspiration-start valve 26 and the venturi 24 are installed in the delivery conduit 14, the latter at ya location downstream of the valve 26, Iand arranged so that ow to the delivery means 18 is through them. The sensing unit 22 is operatively connected to the Ivent valve 20 and coupled to two pressure-sensing elements in the delivery conduit 14. In this illustrative case, the pressure-sensing elements comprise a port 28 at the throat of the venturi 3 24 and a Pitot tube 3i) centrally within the conduit 14 at a location upstream of the inspiration-start valve 26 and with its opening facing upstream.

In general, the function of the control means is to seat the vent valve 20 responsive to a slight negative pressure in the delivery conduit 14 adjacent the delivery means 18, such as is produced when a patient makes an inspiratory effort in normal breathing. This serves to initiate inspiration. The control means also functions to maintain the valve 20 seated and thus to continue inspiration so long as the ow through the delivery conduit 14 to the delivery means 18 exceeds the predetermined terminal ow. As the patient becomes fully ventilated, the ow rate drops, eventually dropping to the terminal ilow whereupon the valve 20 is permitted to open to terminate inspiration.

It will be appreciated from the foregoing that the apparatus of the invention is pressure-sensitive to initiate inspiration and flow-responsive to terminate inspiration.

Turning now to the construction details of the individual elements of the apparatus, the vent valve 20 is of the inatable-dellatable type. It is disposed in close proximity to the vent opening 16 at the end of the main conduit 12. Thus, when pressurized gas is supplied intermittently to the interior of the valve 2t), ination occurs to move it into seated relationship with the conduit end to close ott the opening 16.

Pressurized gas is supplied for operating the vent valve 20 by valve-supply conduit 34 coupled to the main conduit 12. In order to achieve the desired cyclic operation of the valve 20, the valve supply conduit 34 is provided With a bleed orifice 36 and an internal restriction 38. With this arrangement, when the bleed orice 36 is closed, pressurized gas is supplied by the conduit 34 to seat the vent valve 2t) and thereby close the opening 16. In further regard to closure of the vent valve 2d, it is to be noted that the eective area thereof is larger than that of the opening 16 in the conduit 12. Accordingly, when the pressure within lthe valve 20 is lapproximately equal to, or even slightly less than that within the conduit 12, the valve 20 will close and remain closed.

Opening -of the vent valve 20 to permit main stream tlow from the source to the atmosphere takes place when the bleed orifice 36 is open. The internal restriction 38 is sized in relation to the orifice 36 to enable such opening notwithstanding the fact that pressurized gas is upplied continuously through the valve supply conduit Rapid and positive closure of the vent valve upon closing of the bleed orice 36 is assured by virtue of the valve supply conduit 34 being coupled to the main conduit 12 by a pitot tube 40. As may be seen in the drawing, the tube 40 is mounted centrally of the conduit 12 at a location ldownstream of the coupling to the delivery conduit I14 and with its opening facing upstream. During periods of ow through the main conduit 12 to the atmosphere, i.e., when the vent valve 20 is inoperative, the pressure signal supplied by the Pitot tube is the sum of the static pressure within the conduit and the dynamic pressure due to the impact of the owing gas against the opening of the tube 40. Thus, the desired rapid and positive closing of the valve 2t) is accomplished upon closure of the bleed orifice 36.

Intermittent closure of the bleed oriiice 36 is by a control valve member 42 mounted on a rocker arm 44. The arm 44 is pivotally mounted at 46 and arranged for rocking movement to move the valve member 42 into and out of closing relationship with the bleed orifice 36. A light compression spring `48 yieldably urges the arm 44 in a direction to move the valve member 42 into and maintain it in such relationship.

As previously noted, the sensing unit 22 is operatively connected to the vent valve 20. Specifically, the sensing unit 22 actuates the rocker arm 44 and thereby moves the valve member 42 into and out of closing relationship with the bleed orice 36, so as to cycle the apparatus between its inspiratory and expiratory modes of operation.

The sensing unit 22 includes a housing 50 with an internal chamber divided by a horizontal, flexible diaphragm 52 into an upper or iirst compartment 54 and a lower or second compartment 56. The diaphragm 52 is movable therein between a normal or expiratory position, illustrated in FIGURE l, and a depressed or inspiratory position, illustrated in FIGURE 2. Movement from the expiratory toward the inspiratory position is yieldably resisted by a light compression spring 5S, the action of the spring S8 being at least suicient to overcome the inuence of the spring 48 tending to urge the diaphragm toward its inspiratory position.

The diaphragm 52, in turn, is linked to the rocker arm 44 by a slidable rod 60 xed to the diaphragm 52 at one end and bearing on the underside of the rocker arm 44 at its opposite end. As may be seen in the drawing, the expiratory position of the diaphragm S2 (FIG- URE 1) corresponds to the position of the rocker arm 44 wherein the valve member 42 is out of closing relationship with the bleed orifice 36; the inspiratory position of the diaphragm 52 (FIGURE 2) corresponds to the position of the rocker arm 44 wherein the valve member 42 is in closing relationship with the orifice 36.

It will be appreciated that with the specilied mounting of the diaphragm 52 it is in a balanced condition in its expiratory position of FIGURE l. An unbalancing force tending to move it toward its inspiratory position of FIGURE 2 is produced when a pressure differential exists between the compartments 54 and 56. In particular, the diaphragm 52 is moved downwardly toward its inspiratory position ywhen the pressure differential is suiicient to overcome the biasing force of the spring 58. Adjustment of the pressure differential required to so move the diaphragm 52, or, in other words, sensitivity adjustment is accomplished by an adjustment screw 62 mounted on the housing 50 and bearing on the end of the spring 58, Rotation of the screw 62, of course, serves to vary the compressed spring length and, hence, the biasing force.

The compartments 54 and 56 are coupled to the pitot tube 30 and the port 28 at the throat of the venturi 24 by pressure-sensing conduits 64 and 66. The pitot tube 39, like the pitot tube 40, is positioned so that during periods of flow, in this instance, through the delivery conduit 14, the pressure transmitted to the tirst compartment 54 is the sum of the static pressure within the conduit 12 and the dynamic pressure due to the ow. Increases and decreases in ilow produce corresponding increases and decreases in the dynamic component. Thus, during periods of flow through the conduit 14, the pressure sensed by the pitot tube 30 is relatively increased as compared to the static pressure within the conduit 14. On the other hand, as is well known in the art, flow through a venturi produces a velocity increase and a corresponding pressure drop at the throat. The extent of the drop varies in accordance with ow, the greater the flow the greater the pressure drop. Thus, during flow through conduit 14, the pressure sensed at the port 28 at the throat of the venturi 24 is reduced with respect to the static pressure in the conduit and such pressure is transmitted by the conduit 66 to the second compartment 56.

At high flow rates, the pressure differential across the diaphragm 52 is substantial and serves to hold the latter securely in its inspiratory position of FIGURE 2. This, of course, stems from the fact that at such ow rates, the pressure sensed by the pitot tube 30 is substantially above the static pressure within the conduit 14, while that sensed by the port 22 at the throat of the venturi 24 is substantially below such static pressure.

As flow through the delivery conduit 14 decreases, the difference n pressures sensed by the pitot tube 30 and port 2S and transmitted to their respective compartments 54 and 56 correspondingly decreases. Accordingly, the unbalancing force on the diaphragm maintaining it in its inspiratory position of FIGURE 2 likewise decreases. When the ow rate drops to terminal ow, the pressure dilierential is insuicient to hold the diaphragm down and it moves back to its expiratory position of FIG- URE 1 under the biasing force of the spring 58.

Should it be desired to vary the terminal flow, this can be readily accomplished, among other Ways, by changing the configuration of the venturi 24. In this connection, it is also to be observed that the spring 58 could be made suiciently strong to significantly alect terminal ow. However, in the case of the apparatus of the invention, this is an undesirable expedient because it would, in turn, impair the normally desired high sensitivity of the unit. To avoid any such undesirable interrelationship between these operating characteristics, the diaphragm 52 is made very large in effective area and the spring 5S, as previously noted, is relatively light in action.

The inspiration-start Valve 26 is provided for the purpose of enabling the inspiratory phase of operation to be initiated upon a negative pressure being drawn in the conduit 14 adjacent the delivery means 18. As may be seen in FIGURE 1, this valve is located in the conduit 14 between the pitot tube 3i) and the port 28. It functions to block dow through the conduit 14 responsive to such a negative pressure when the vent valve 2G is inoperative. By virtue o this valving function, negative pressure is prevented from acting through the pitot tube 30 and conduit 64 on the upper side of the diaphragm 52, and accordingly, from counter-balancing the desired effect of such negative pressure acting through the port ZS and conduit 66 on the lower side of the diaphragm. Therefore, the diaphragm 52 moves downwardly to its inspiratory position of FIGURE 2, responsive to such a negative pressure being drawn by the patient in the conduit 14 adjacent the delivery means.

The inspiration-start valve 26 is provided with a housing 68 forming a valve chamber 70 with an inlet 72 and an outlet 74 coupled to upstream and downstream portions, respectively, of the conduit 14. The inlet comprises a tubular member projecting into the chamber 70 and having a valve seat 76 at its terminal end. Cooperable with the seat 76 to block the opening from the inlet member to the chamber 70 is a diaphragm-type closure element 78 disposed within the chamber and having a cross-sectional area larger than that of the seat. Referring to FIGURE 1, it may be seen that one side of the closure element 78 is exposed to ambient pressure through a passage 80 in the wall of the housing 68, While the opposite side is closely adjacent the seat 76. The closure element 78 is formed of a resilient, exible material in order that it is readily movable into and out of sealing relationship with the seat 76.

As is apparent from the construction of the inspiration-start valve 26, assuming that the pressure within the conduit 14 upstream of the valve is approximately equal to ambient pressure, a negative pressure within the chamber 70 serves to `draw the closure element onto the seat 76. This, in turn, precludes such pressure from acting through the upstream portion of the conduit 14 and, specitically, from acting on the upper side of the diaphragm 52 of the sensing unit 22. When a positive pressure exists within the upstream portion of the conduit 14, as during intermittent periods of ow to the delivery means 18, the closure element 78 is simply forced away from the seat 76.

Flow-directing means 82 are provided to insure that the pressure in the conduit 14 adjacent the pitot tube 38 is approximately equal to ambient pressure when the vent valve 20 is inoperative. In other words, such a pressure condition is desired during the expiratory phase of operation when gas from the source 10 is being exhausted to the atmosphere through the vent opening 16.

In the illustrative case, the now-directing means 82 comprises a tubular member with an elongated main body portion 84 and an outwardly daring, frusto-conical end portion 86. It is disposed within the main conduit 12 adjacent the junction with the delivery conduit 14. The end portion `S6 is fixed to the wall of the main conduit 12 at a location upstream of the junction ofthe two conduits, and the body portion 84 projects downstream past the junction.

When the vent valve 20 is inoperative, the flow-directing means 82. serve to channel the flow past the junction of the conduits 12 and 14 and thereby achieve the desired pressure condition. On the other hand, when the vent valve 2t) is operative to block the vent opening 16, pressurized gas is permitted to flow through the delivery conduit 14 by virtue of the body portion 84 of the tubular member being spaced radially inwardly of the wall of the conduit To enable the patient to exhale to the atmosphere during the expiratory phase of operation, an exhalation passage 88 is provided in the conduit 14 adjacent the delivery means 13. The passage 88 is closed during the inspiratory phase of operation by an inflatable-deatable type exhalation valve 90. In the illustrative case, the lower end of the valve 90 is positioned closely adjacent the opening in the passage 8S. Therefore, when a slight negative pressure is drawn in the conduit 14 adjacent the delivery means, the valve 90 is drawn down into a seated position to block the opening passage 88.

Positive pressure is supplied to the interior of the exhalation valve 90 to maintain it securely seated throughout the inspiratory phase through an auxiliary conduit 92 internally restricted at 94 and coupled to the pressuresensing conduit 64. Thus, during inspiration, the pressure within the interior of the exhalation valve 90 is at least equal to and normally greater than the static pressure within the conduit 14 for reasons previously explained. As may be seen in FIGURE 1, the cross-sectional area of the exhalation valve 90 is greater than the area of the opening in the passage 88. Thus, even though the pressure within the interior of the valve should be no greater than that within the adjacent portion of the conduit 14, it will remain securely closed.

A check valve 96 is provided in the conduit 14 at a location between the inspiration-start valve 26 andthe venturi 24. The check valve 96 operates during expiration to block backrlow through the conduit 14, thereby insuring that the exhalation valve 90 remains open during that phase. With this arrangement, the patient exhales through only the exhalation passage 88. Flow in the opposite direction through conduit 14 to the delivery means during inspiration is in no way impaired by the check valve 96.

The source 10 of pressurized gas may, by way of example, comprise a pump for compressing ambient air or a tank of compressed gas, such as air or oxygen. As is conventional, the source 10 embodies suitable regulation apparatus for insuring that the gas supplied to the patient is at a mild control pressure no greater than a preset maximum. Preferably, for ilexibility of use, the regulation apparatus is adjustable to enable the maximum pressure to be preset within a safe range. Reference is made in this connection to my U.S. Patent No. 3,221,733, entitled Pressure Breathing Therapy Unit, which discloses a -pump and regulation apparatus highly suitable for this purpose.

Operation To ready the apparatus of the invention for use in administering IPPB therapy, it is simply necessary to preset the source pressure at the desired level, and to adjust sensitivity by means of the adjustment screw. The apparatus is then put in operation by activating the source 10 to supply gas through the conduit system. The control means then functions in response to a negative pressure in the conduit 14 adjacent the delivery means and, thereafter, in response to flow through the condiut 14 dropping to the terminal flow to cycle the apparatus into inspiratory and expiratoty modes of operation, respectively.

As previously explained, the apparatus is normally in its expiratory mode of operation, as in FIGURE 1. The diaphragm 52 is then in its expiratory position, so that the vent valve 20 is inoperative. Pressurized gas supplied by the pitot tube 46 to the valve supply conduit 34 coupled thereto is bled off to the atmosphere through the bleed orifice 36 at a rate such that the vent valve 20 remains inoperative. Flow is directed in the main conduit 12 by the flow-directing means toward the vent opening 16 and gas is exhausted to the atmosphere through that opening. With the liow so directed, the pressure in the delivery conduit 14 adjacent the connection with the main conduit and, in particular, adjacent the pitot tube 30, is approximately equal to ambient pressure. Thus, the exhalation valve 90 is in a relatively deflated condition and the associated passage 88 is unobstructed. The apparatus remains in this operative state, with gas from the source being exhausted to the atmosphere, until the patient exerts an inspiratory effort to initiate that phase of the breathing cycle;

Assuming the delivery means 18 to have been coupled to the patients respiratory system, e.g., a face mask irstalled, a slight inspiratory effort, as in normal breathing, cycles the apparatus into its inspiratory mode of operation. The degree of effort required, of course, depends upon sensitivity adjustment. Such an effort draws a negative pressure in the portion of the conduit 14 adjacent the delivery means 18, the effect of which initially is to draw the exhalation valve 90 onto its seat to block the passage 88 and to draw the closure element 78 of the inspirationstart valve 26 onto its seat 76 to block off the upstream portion of the conduit system. Such negative pressure is then transmitted through the Apressure-sensing conduit 66 to the second compartment 56 of the sensing unit to produce an unbalancing force on the diaphragm 52, permitting it to move to its inspiratory position of FIGURE 2 in opposition to the biasing force of the spring 58.

The reaction of the sensing1 unit 22 to the patient effort, in turn, permits the valve member 42 supported on the rocker arm 44 to move into closing relationship with the bleed orifice 36. Rapid and positive closure of the vent valve 22 to block the vent opening 16 follows because of the action of the pitot tube 40 insensing a positive pressure which is the sum of static and dynamic pressures in the main conduit 12.

Closing of the vent valve causes flow to commence through the delivery conduit 14 to the patient. Upon commencement of such ow, a positive pressure is sensed by the pitot tube 38 in the delivery conduit 14, and a positive pressure signal is transmitted through conduits 64 and 92 to the exhalation valve 9G to seat it and block the passage 88. As set forth above, during periods of flow through the conduit 14, the pressure sensed by the pitot tube and port 28 at the throat of the venturi 24 are relatively increased and decreased, respectively, relative to the static pressure within the conduit. The difference in such pressures, which are transmitted to the associated compartments 54 and 56 of the sensing unit, is made use of to maintain the diaphragm 52 in its inspiratory position.

Near the start of the inspiratory phase, the patients requirement is at its peak, and hence the flow is likewise at a peak. In this connection it is to be noted that the peak flow capacity of the present system is very high, since none of the elements in the flow path from the source 1) to the delivery means 18 appreciably throttlcs flow. While the cross-sectional area of the path is decreased at the throat ofthe venturi 24, such a device has very little throttling, effect, as is well know in the art.

At high flow rates, such as exist near the start of the inspiratory phase, the pressure differential across the diaphragm 52 is more than ample to maintain it in its insipratory position. Ae the inspiratory phase progresses, the flow rate drops, so that the pressure differential correspondingly decreases. Eventually the flow rate drops to the terminal fiow where, as previously noted, the differential is insufficient to overcome the biasing force of the spring 5S. The diaphragm 52 then moves back to its expiratory position of FIGURE 1 to terminate the inspiratory phase or, conversely, to initiate the expiratory phase of the cycle.

With regard to terminal flow, it may be very low in the case of the apparatus of the invention, thereby insuring full and even ventilation. Moreover, this desirable operating characteristic is attained without adversely affecting either peak ow capacity or sensitivity. This results from the use of the pitot tube 30 and the port 28 at the throat of the venturi 24 as sensing elements. As long as any appreciable flow is taking place to the patient, the pressures sensed by these elements diler substantially.

Responsive to the diaphragm 52 moving back to its normal position of FIGURE l, the valve member 42 moves away from the orifice 36 to permit it to bleed pressurized gas from the vent valve 20. Once this has occurred, the vent valve 2t, is again rendered inoperative, so that gas from the source 10 is exhausted through the vent opening 16 to the atmosphere, Simultaneously, pressurized gas is bled from the exhalation valve to open the passage 88 and permit the patient to exhale freely to the atmosphere. DarinC the expiratory phase, the check valve 96 prevents backllow through the conduit 14, as might otherwise pressurize the exhalation valve 90 and impair free exhalation. This completes a given cycle 0f operation and the apparatus remains in its expiratory phase, as in FIGURE 1, until the patient exerts another inspiratory effort.

It is significant to note that the apparatus of the invention not only is highly satisfactory in operation, but is inherently very reliable. lt embodies no critical moving parts. Of the various elements of the apparatus, none is of the type that is prone to malfunction. Moreover, none need be manufactured to close tolerances or in accordance with any costly manufacturing procedures. On the contrary, the elements are all readily adapted to be formed economically in accordance with mass production techniques.

While one embodiment of the invention has been illustrated and described in fair amount of detail, it will be understood that this is only by way of illustration and that various changes in the constructions and arrangements of the various elements may be made without departing from the spirit and scope of the invention.

I claim: 1. In respiration apparatus including a source of pressurized gas and delivery means, a patient-controlled system for supplying intermittently gas from said source to said delivery means, comprising:

main conduit means coupled to said source and having a vent opening to the atmosphere;

delivery conduit means coupled at its opposite ends to said main conduit means and to said delivery means;

vent valve means adapted to be cycled between an inoperative condition, wherein flow of gas takes place from said source through said main conduit means to the atmosphere through said vent opening, and an operative condition, wherein the flow of gas is from said source through said main and delivery conduit means to said delivery means;

a venturi in said delivery conduit means; and

control means including pressure-sensing means coupled to said venturi at the throat thereof and to said delivery conduit means at a location spaced from said venturi; means connecting said control means and said vent valve means to cycle said vent valve means between said inoperative and Said operative condition, and means for preventing a negative pressure signal in said delivery conduit means adjacent said delivery means from acting on said control means through the coupling to said delivery conduit means spaced from the venturi, but permitting such signal to act on said control means through the coupling at the throat of said venturi, said control means being responsive to a predetermined negative pressure signal in said delivery conduit means adjacent said delivery means for cycling said vent valve means to its operative condition and to a predetermined terminal flow through said delivery conduit means independent of absolute pressures therein for cycling said vent valve means to its inoperative condition.

2. In respiration apparatus including a source of pressurized gas and delivery means, a patient-controlled system for supplying intermittently gas from said source to said delivery means comprising:

a main conduit coupled to said source and having a vent opening to the atmosphere;

vent valve means operative intermittently to close said vent opening;

a delivery conduit coupled at its opposite ends to said delivery means; how-directing means in said main conduit adjacent the junction of said delivery conduit for directing liow in said conduit from said source past the junction of said delivery conduit and out said vent opening when said vent valve means is inoperative, whereby the pressure in said delivery conduit adjacent the junction of said main conduit during such iiow is approximately equal to atmospheric pressure; an inspiration-start valve in said delivery conduit responsive to a negative pressure therein on the downstream side thereof when said vent valve means is inoperative to block tiow through said delivery conduit; a venturi in said delivery conduit intermediate said inspiration-start valve and said delivery means;

and a diaphragm-type sensing unit including a chamlber divided by a movable diaphragm into iirst and second compartments coupled to said delivery conduit at a location upstream of said inspiration-start valve and to said venturi at the throat thereof, respectively, said diaphragm including means connecting said sensing unit and said vent valve means; said diaphragm being movable between an expiratory position, wherein said vent valve means is inoperative, and an inspiratory position, wherein said vent valve means is operative to close said vent opening and cause iiow to take place through said main and delivery conduits from said source to said delivery means.

3. The subject matter of claim 2, wherein said inspiration-start valve is also responsive to a positive pressure in said delivery conduit when said vent valve means is operative to permit flow through said delivery conduit.

4. The subject matter of claim 2, wherein said iirst compartment is coupled to said delivery conduit by means including a pitot tube disposed in said delivery conduit with its opening facing upstream.

5. The subject matter of claim 2, including means biasing said diaphragm toward its expiration position.

6. The subject matter of claim 5, wherein said biasing means is a spring; and

including means accessible from the exterior of said sensing unit for adjustably establishing the rate of said spring.

7. The subject matter of claim 2, wherein said vent valve means is operated by pressurized gas from said source delivered thereto by means including a pitot tube disposed in said main conduit with its opening facing upstream and an auxiliary conduit with a bleed orifice therein, said vent valve means being operative to close said vent opening when said bleed orifice is blocked and inoperative when said bleed oriiice is open; and

including means operatively connected to said sensing unit and operated thereby for blocking said bleed orifice when said diaphragm is in its inspiratory position, said bleed orifice being open when said diaphragm is in its expiratory position.

8. The subject matter of claim 2, wherein said flowdirecting means comprises a tube of reduced cross-section in relation to the cross-section of the main conduit disposed generally longitudinally within the latter with its outer periphery spaced radially inwardly from the inner periphery of the main conduit, said tube being sealingly joined adjacent one end to said main conduit at a location upstream of the junction of said main and delivery conduits and having its opposite end extending .past said junction.

9. In respiration apparatus including a source of pressurized gas and delivery means, a patient-controlled system for supplying intermittently gas from said source to said delivery means, comprising:

a main conduit coupled at one end to said source and having a vent opening at the opposite end to the atmosphere;

a vent valve seat at the opposite end of said main conduit;

an inatable-deflatable type vent valve cooperable with said seat in an intiated condition to block said vent opening and in a deflated condition to .permit iow from said source through said Vent opening to the atmosphere;

a pitot tube in said main conduit with its opening facing upstream;

a valve-supply conduit coupled to said pitot tube and to said vent valve and having an internal restriction and formed with a bleed passage sized in relation to the restriction so that when the bleed passage is open said vent valve is deilated, said vent valve being iniiated when said bleed passage is closed;

a delivery conduit couped at its opposite ends to said main conduit and to said delivery means;

flow-directing means in said main conduit adjacent the junction of said delivery conduit for directing flow in said main conduit from said source past the junction of said delivery conduit `and out said vent opening when said vent valve is deiiated, whereby the pressure in said delivery conduit adjacent the junction of said main conduit during such iiow is approximately equal to atmospheric pressure;

an inspiration-start valve in said delivery conduit operable intermittently to block flow therethrough when the pressure in said delivery conduit upstream thereof is approximately equal to ambient pressure and the pressure in said delivery conduit downstream thereof adjacent said delivery means is less than ambient pressure;

a diaphragm-type sensing unit including a chamber separated into iirst and second compartments by a diaphragm movable between expiratory and inspiratory positions;

sensing means in said delivery conduit upstream of said inspiration-start valve;

a venturi in said delivery conduit between said inspiration-start valve and the delivery means havling a pressure-sensing port at the throat thereof;

a rst sensing conduit coupled at its opposite ends to said sensing means and to said first compartment;

a second sensing conduit coupled at its opposite ends to said part at the throat of said venturi and to said second compartment;

valve means operatively connected to said diaphragm, said valve means being operative to close said bleed passage when said diaphragm is in its inspiratory position and to permit tiow through said bleed passage when said diaphragm is in its expiratory position;

and means biasing said diaphragm toward its expiration position, said diaphragm being responsive to a slight negative pressure delivery means to overcome the action of said biasing means and move from its eX- piratory towardits inspiratory position.

10. The subject matter of claim 9, wherein said sensing means comprises a pitot tube with its opening facing upstream.

References Cited UNITED STATES PATENTS 2,468,741 5/1949 Emerson 12S-145.7

Haverland 12S-145.8 Cummins 12S-142.5 Wilson 12S-145.8

Beasley 12S-145.8 McDonough 12S-142 RICHARD A. GAUDET, Primary Examiner. i

K. L. HOWELL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0. 3,385 ,295 May 28, 1968 Noel F. -Beasley It is certified that error appears in the above identified Y patent and that'sad Letters Patent are hereby corrected as' shown below:

line 21, after "said" insert main conduit 4and to said line Z4, after "said" Signed and sealed this 18th day of November 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLEB JR.

EdwardM. Fletcher, Ir. r Y

C Commissioner of Patents Attesting Officer 

1. IN RESPIRATION APPARATUS INCLUDING A SOURCE OF PRESSURIZED GAS AND DELIVERY MEANS, A PATIENT-CONTROLLED SYSTEM FOR SUPPLYING INTERMITTENTLY GAS FROM SAID SOURCE TO SAID DELIVERY MEANS, COMPRISING: MAIN CONDUIT MEANS COUPLED TO SAID SOURCE AND HAVING A VENT OPENING TO THE ATMOSPHERE; DELIVERY CONDUIT MEANS COUPLED AT ITS OPPOSITE ENDS TO SAID MAIN CONDUIT MEANS AND TO SAID DELIVERY MEANS; VENT VALVE MEANS ADAPTED TO BE CYCLED BETWEEN AN INOPERATIVE CONDITION, WHEREIN FLOW OF GAS TAKES PLACE FROM SAID SOURCE THROUGH SAID MAIN CONDUIT MEANS TO THE ATMOSPHERE THROUGH SAID VENT OPENING, AND AN OPERATIVE CONDITION, WHEREIN THE FLOW OF GAS IS FROM SAID SOURCE THROUGH SAID MAIN AND DELIVERY CONDUIT MEANS TO SAID DELIVERY MEANS; A VENTURI IN SAID DELIVERY CONDUIT MEANS; AND CONTROL MEANS INCLUDING PRESSURE-SENSING MEANS COUPLED TO SAID VENTURI AT THE THROAT THEREOF AND TO SAID DELIVERY CONDUIT MEANS AT A LOCATION SPACED FROM SAID VENTURI; MEANS CONNECTING SAID CONTROL MEANS AND SAID VENT VALVE MEANS TO CYCLE SAID VENT VALVE MEANS BETWEEN SAID INOPERATIVE AND SAID OPERATIVE CONDITION, AND MEANS FOR PREVENTING A NEGATIVE PRESSURE SIGNAL IN SAID DELIVERY CONDUIT MEANS ADJACENT SAID DELIVERY MEANS FROM ACTING ON SAID CONTROL MEANS THROUGH THE COUPLING TO SAID DELIVERY CONDUIT MEANS SPACED FROM THE VENTURI, BUT PERMITTING SUCH SIGNAL TO ACT ON SAID CONTROL MEANS THROUGH THE COUPLING AT THE THROAT OF SAID VENTURI, SAID CONTROL MEANS BEING RESPONSIVE TO A PREDETERMINED NEGATIVE PRESSURE SIGNAL IN SAID DELIVERY CONDUIT MEANS ADJACENT SAID DELIVERY MEANS FOR CYCLING SAID VENT VALVE MEANS TO ITS OPERATIVE CONDITION AND TO A PREDETERMINED TERMINAL FLOW THROUGH SAID DELIVERY CONDUIT MEANS INDEPENDENT OF ABSOLUTE PRESSURES THEREIN FOR CYCLING SAID VENT VALVE MEANS TO ITS INOPERATIVE CONDITION. 